At which time it appeared that NY State (where I tested this) was one of the states that had some sort of "soft-tone" requirement. Apparently that is no longer the case.
As some of you have pointed out in our recent post, Using your cell phone as your home phone comes with a risk, some states do require local carriers to maintain a "soft" or "warm" dial tone, which allows you to call 911 on a line that has been disconnected or is otherwise inactive.
An up-to-date-list of affected states is elusive; we struck out in obtaining one from the FCC and some industry groups. However, the following are likely states for some form of soft-tone requirement; we assembled the list from data in an FCC report published in 2000 (Adobe Acrobat software required) and a North American Numbering Council (NANCE) report published in 2002 (link requires Microsoft Word or compatible word processing software).
However, we can't confirm that coverage is in effect in all those states today. Also, some soft-tone coverage is limited, in time or other respects. For example, according to the NANCE report, emergency service in Oklahoma is mandated for only 30 days following the suspension of service. In Ohio, the period is only 14 days.